USRP Audio FM Transmitter with PTT

[palmer]

I am attempting to create a Family Radio Service (FRS) radio using LabVIEW 2014, the Modulation Toolkit, the PC's soundcard, and a NI USRP 2920.   I'm trying to build it along the lines of the Bursty Demo found on this forum but this is an analog voice application instead of digital data so there's a lot of changes.   I am fairly sure that the use of queues is necessary based on the Bursty Demo discussions but I'm not that familiar with them.  There are a few challenges in implementing an FRS transceiver but the first thing I am stuck on is I cannot get the soundcard to capture audio when the Push To Talk (PTT) button is pushed (in the vi using queues).  The USRP transmits for a bit then stops but there is no indication that the audio is being captured.  If I don't use a queue based architecture (no_queue version) it will acquire audio and transmit for the number of samples/ch then quits.  At least that validates the audio capture and Tx is working.

So, how do I get it to capture microphone audio and transmit for as long as the PTT is pressed then wait for the next PTT?   The next step will be to add in a receive while not transmtting but I'm not there yet.  I've attached both vi's, one with the queue structure and one without.

This would be a really cool and informative demo to have on here once it's working.... Any suggestions?

[ErikL]

This is a mutirate DSP application.  FRS uses a 12.5kHz banwidth.  I would break up the acquired audio into frames, add the CTCSSS tone, and then FM modulate the signal.  The frame can then be passed to the USRP via the NI-USRP driver.  If the frame size set to about 10ms, then you should perceive 'real-time' PTT performance.